What it does:
This bug enables Blood DKs to emit massive(+100k Hps) self heals through use of a level 85 weapon.
How it's caused:
Souldrinker(level 85 weapon) can proc off the DK talent "Rolling blood".
The more 'mobs' your rolling blood talent spreads to, causes the weapon to have a chance to proc on 1 or all of them.
Say I have 100 mobs on me >> I outbreak diseases on one > Then blood boil spam.
The souldrinker will proc at least 15 times per blood boil. Causing around 15-30k self heals(Depends on HP/Vamp Blood) to a total of about 300k healing. Weapon enchants also proc like crazy if they don't have an ICD.
Here's a video of it in action: How to get Sanguinarian achievement easily - WoW MoP - YouTube
Note the diseases were applied a bit late, so the souldrinker wasn't proccing from the blood boils until around 00:31.
I discovered this by myself a few weeks ago, and I don't know anyone else who does it.